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<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-E61A931D-6E66-5E17-AE61-ABFB74CB8EF2" xml:lang="en"><title>Life

cycle of active objects</title><shortdesc>This document describes the life cycle of an active objet.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The diagram illustrates the life-cycle of an active object. </p>

<fig id="GUID-BF465AB5-B007-5F44-9AF7-DA0963AE3BDE">

<title>Flow diagram showing the life cycle of an active object</title>

<image href="GUID-36F18DC4-7BD0-59C6-95E9-8FD945B86D7E_d0e325366_href.png" placement="inline"/>

</fig>

<p>Procedural flow follows the black arrows; control is transferred along

the blue links, as follows:</p>

<ul>

<li id="GUID-3E3558A3-8C64-515B-A024-81586B472985"><p>the main program creates

and installs an active scheduler</p> </li>

<li id="GUID-15AE6C3A-5CF7-5711-951A-6FFC8CB6ED27"><p>active objects are created;

their constructors ensure that every active object is added to the active

scheduler (which keeps a reference to the object in its queue)</p> </li>

<li id="GUID-9428DF85-02A3-56C2-A145-604A0356A166"><p>an active object is

called to issue an initial request. This sets the object's <codeph>iActive</codeph> true

(indicating a request was issued but not yet completed) and schedules the

underlying service, which sets the object's <codeph>iStatus</codeph> to <codeph>KRequestPending</codeph>.

(If this step is omitted, no service will be requested, so no handler will

be invoked and hence the active scheduler will wait forever in its loop, never

calling any object's <codeph>RunL()</codeph>)</p> </li>

<li id="GUID-48E77554-3EF4-5313-969A-12D3426DA502"><p>the active scheduler

is started. This now takes over; control is only returned to the main program

for termination when the active scheduler is stopped</p> </li>

<li id="GUID-E697E0CF-65F0-5AFD-8201-ADC6A791D98C"><p>when a requested service

completes, it's handler terminates by signaling service completion; this alters

the associated active object's <codeph>iStatus</codeph> </p> </li>

<li id="GUID-CDD9242D-9540-5DC0-A948-8914F2AEF905"><p>when any service handler

signals completion, the active scheduler tests each object in its queues for

one with <codeph>iActive</codeph> true (request not completed) and <codeph>iStatus</codeph> not

set to <codeph>KRequestPending</codeph> (i.e. the request has been handled) </p> </li>

<li id="GUID-98980800-03DA-5623-9305-94609FBE9788"><p>if the active scheduler

finds an object with the above conditions, it sets <codeph>iActive</codeph> false

and calls the object's <codeph>RunL()</codeph> </p> </li>

<li id="GUID-CFC4609C-3FED-538E-9555-1A90114876A3"><p>the <codeph>RunL()</codeph> may

reschedule the request (so that the handler is again invoked when the requested

service completes and the cycle continues.) or may stop the active scheduler,

returning control to the main program for termination.</p> </li>

</ul>